This invention relates, to general, to microwave hybrids for use in Monolithic Microwave Integrated Circuits (MMIC), and more specifically, to 180 degrees broadband MMIC hybrids.
One hundred-eighty degree hybrids are common elements found in mixers which modulate RF (radio frequency) input signals with signals from local oscillators to output IF (intermediate frequency) signals. One hundred-eighty degree hybrids are further used in a variety of circuits as basic circuit elements. There are many types of 180 degree hybrids for use in the frequencies up to the low megahertz range. Such hybrids use various methods of construction such as the Marchand Balun hybrids, and often incorporate ferrite elements to obtain bandwidth performance. However, hybrids constructed by such conventional methods are not usable with microwave circuits, or they are limited to extremely high frequencies (above 25 GHz), particularly when incorporated on GaAs (Gallium Arsenide) media for MMIC circuits. Additionally, ferrite cannot be used on MMIC circuits. MMIC circuits are suited to lumped and distributed elements due to the extremely small circuit area inherent with GaAs media. Those 180 degree hybrid MMIC circuits which have been constructed with lumped elements have, thus far, been limited to very narrow bandwidths (less than 5-10%), and suffer in both phase and amplitude performance.